1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine and a printer that uses an electrophotographic system or an electrostatic recording system.
2. Description of the Related Art
Among image forming apparatuses, digital laser beam printers of a so- called electrophotographic system have been known. In a development device equipped in the image forming apparatus, a one-component developer containing magnetic toner as a main component, or a two-component developer containing non-magnetic toner and magnetic carrier as main components has been used. In particular, in the image forming apparatus that forms a full-color or multi-color image, the two-component developer has been mainly used from the viewpoint of color of an image or the like.
There is a toner supply control as particular importance in the two-component developer. The two-component developer has the toner and the carrier, and when forming the image, a TD ratio as a ratio of the toner to the carrier changes by consumption of the toner. Since charging characteristics of the toner change depending on the value of the TD ratio, it is required to supply the toner so as to maintain the charging characteristics of the toner. A toner bottle configured to supply the toner is provided separately from the development device, and when there is no toner in the toner bottle, the toner bottle is replaced with a new one.
Furthermore, in recent years, there have been increased demands for size reduction and noise reduction of the image forming apparatuses. For example, as an example of the size reduction, as in US Patent Application Publication No. 2006/165423 A1, and Japanese Patent Laid-Open No. 2011-048201, in an image forming apparatus that forms a full color image, a size reduction of a supply motor configured to turn a toner bottle is achieved by using two colors by one motor. Here, in some cases, the supply cannot be kept up depending on the toner consumption of the common two colors, and since the TD ratio of the two-component developer is lowered at that time, the supply is implemented by providing downtime.
Furthermore, as examples of the noise reduction, by lowering the number of rotations of the supply motor, it is possible to use the smaller motors, thereby reducing the sound. Even at this time, in some cases, the supply cannot be kept up depending on the toner consumption, and since the TD ratio of the two-component developer is lowered at that time, it is necessary to carry out the supply by providing the downtime.
However, in some cases, the supply cannot be kept up depending on the toner consumption. In this case, a control is performed such that the control (forced supply sequence) of implementing the supply by providing the downtime is input, but the following problems may occur.
When a remaining amount of toner in the toner bottle decreases (just before toner absence), the toner capable of being supplied into the development device decreases. For this reason, even in the image with less toner consumption, the TD ratio of the two-component developer is lowered. In this case, since the amount of toner supply required for the image forming apparatus increases, the supply is not kept up for the required amount of supply, and the forced supply sequence starts.
However, even if the forced supply sequence is implemented, since the amount of toner to be supplied to the development device is small, the TD ratio of the two-component developer does not rise. For this reason, in some cases, the forced supply sequence may be repeatedly performed more than necessary. In this case, there has been a problem in that the downtime due to the forced supply sequence occurs frequently until “toner absence” is displayed.